The fabrication of integrated circuits (IC) in the semiconductor device manufacturing industry typically employs plasma to create and assist surface chemistry necessary to remove material from and deposit material to a substrate. In general, plasma is formed within a plasma processing system under vacuum conditions by heating electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the heated electrons can have energy sufficient to sustain dissociative collisions and, therefore, a specific set of gases under predetermined conditions (e.g., chamber pressure, gas flow rate, etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the processing system (e.g., etching processes where materials are removed from the substrate or deposition processes where materials are added to the substrate).
Subsequent to the use of plasma for IC fabrication, plasma charging damage has posed a very serious threat to the yield of acceptable devices when exposed to a processing plasma. As described above with regards to plasma processing, highly energetic particles, such as different ions, electrons, and photons, bombard the surface of the substrate and, depending on the nature of the material structures formed on the substrate, this energetic interaction with the substrate surface can lead to non-homogeneous charge accumulation and other forms of structural damage, either of which can be catastrophic to the ICs formed thereon. For example, substrate charging damage can manifest as physical damage to crystalline silicon by energetic ions, or electrical damage to SiO2.
Moreover, as described above, substrate charging damage can arise from non-homogeneous charge accumulation due to, for example, electron shading. Electron shading generally occurs when etching high aspect ratio contacts/vias or trenches in dielectric materials and, more recently, electron shading damage has been further exacerbated due to the continual reduction in feature size, and consequent increase in feature aspect ratio. During electron shading, electrons, being mostly isotropic in directionality, tend to have difficulty reaching the bottoms of high aspect ratio features and, therefore, they tend to accumulate at the tops of high aspect ratio features. Conversely, ions are mostly directional and tend to reach the bottoms of these features, hence, leading to electric fields induced by charge separation.
Furthermore, a non-homogeneous charge accumulation can arise from the development of a non-homogeneous plasma in electrical contact with the substrate surface. Consequently, static electric fields can develop laterally across the substrate surface, and they can become of sufficient strength to cause electrical breakdown.
In either case, the formation of static electric fields on the substrate can be sufficient to cause electrical breakdown (or arcing) in more extreme cases, and reduced IC lifetime in less extreme cases, each of which is capable of reducing IC yield.